Upload
others
View
2
Download
0
Embed Size (px)
Citation preview
Extinction
Ani Mardiastuti
Extinction
• The end of an organism or group of taxa
• Moment of extinction the death of the last individual of that species
• Determining moment of extinction is difficult Lazarus taxa: where a species presumed extinct abruptly "re-appears" (typically in the fossil record after a period of apparent absence
Extinction
• Present extinction: very rapid
• High effort to avoid extinction of species
• Lesson learned from the past
Extinctions over the past 600 million years
• Age for the Earth and the rest of the solar system is about 4.54 billion years
• Life began nearly 3.5 billion years ago
• Extinction is a natural phenomenon
• It is estimated that 99.9% of all species that have ever lived are now extinct.
Five Largest Mass Extinction
Five Largest Mass Extinction • Late Ordovician (about 438 million years ago)
• Extinct: 100 families, more than half of the bryozoan and brachiopod species
• Late Devonian (360 mya) • Extinct: 30% of animal families
• Permian - Triassic (245 mya) • Extinct: Trilobites, 50% of all animal families, 95% of all marine
species, and many trees die out • Late Triassic (208 mya)
• Extinct: most early dinosaur families, most synapsids (except mammals); 35% of all animal families die out
• Cretaceous-Tertiary (K-T) (65 mya) • Extinct: about half of all life forms, including the dinosaurs,
may families of fishes, clams, snails, sponges, sea urchins, etc.
Dinosaurs
• Beginning in the Triassic Period and into the late Cretaceous
• Dinosaurs existence: 165 million years Age of the Reptiles
• Why the dinosaurs ‘suddenly’ extinct?
EXTINCTION OF DINOSAURS: some theories
1. UNABLE TO ADAPT TO CHANGES o warmer at the end of the Cretaceous than it is now
2. ASTEROID THEORY (by Luis and Walter Alvarez, 1980) o Great extinctions have occurred at 26 million year intervals o Based on unusually high concentrations of the rare metal,
Iridium, near rock levels close to the level of last dinosaur remains.
3. SUPERNOVA THEORY (exploding star)
4. NEMESIS THEORY
o Death Star, or Nemesis, orbits around the earth, 26 million years cycles
5. PLANET K THEORY (Proposes a tenth planet)
Nemesis Theory
Milky Way: Bima Sakti
Extinction is happening now!
The Sixth (Modern) Extinction • Caused by human
• Rate of extinction:
– Past extinction: between 10 and 100 species per year
– Modern extinction: between 17,000 and 100,000 species per year
• Major causes of modern extinction:
– Habitat loss and fragmentation
– Biological invasion
– Pollution
– Over-harvesting
– Human-induced climate change